There are some basic pieces of etiquette for flying today. Don't be rude or angry with gate agents or flight attendants – your delayed flight is not their fault. Middle seat passengers get both armrests. Keep your shoes on, and never go barefoot.

And we can't believe we have to even say this … but never, ever do this:

Erik Olvera, who works for the Southern Poverty Law Center, captured the disturbing scene Wednesday on board a Delta flight. The passenger guilty of one of flying's grossest sins appears to be in a first class seat in the bulkhead.

Sadly, it's not even the first time this exact same thing has happened on a Delta flight. Behold, yet another flyer scrolling through the entertainment selection with his/her toes!

Let us reiterate: Do not do this. Do not do this flying Delta, American, United, Spirit, Japan Airlines, Garuda Indonesia, or any airline.

Keep your shoes on when you're on a plane, please. Your fellow passengers don't want to smell your feet inside a metal tube. And they certainly don't want to see your toes picking out an episode of Game of Thrones, either.